Dual carburetor



April 23, 1946. s. M. UDALE DUAL CARBURETOR Filed Oct. 11, 19.43

VENTOR.

Patented Apr. 23, 1946 DUAL CARBURETOR smiley M. Udalc, Detroit, Mich assignor to George M. Holley and Earl Holley Application October 11, 1943, Serial No. 505,880

2 Claims.

The object of this invention is to permit an airplane carburetor, adapted to supply air to an engine equipped with a multi-stage supercharger, to be designed big enough normally experienced in a plane flying at from 25,000 to 35,000 feet elevation with the superchargers supplying the greatest volume of air and still not too big to function with the dense air which clings to the surface of the earth and with which air only the minimum amount of supercharging is required. These engines have superchargers which are designed to draw in much more air at high altitudes than at sea level. The dense air available at sea level is controlled by a manually operated throttle to ensure reliable action during the take-oil. At altitudes over 25,000 feet, a second carburetor becomes operative automatically supplying the extra air drawn in by the second-stage supercharger or by the exhaust driven supercharger which then becomes operative. With the superchargers now in use, as they are arranged to draw in more and more air as the air becomes less and less dense. the velocity of fiow through the main venturi ultimately reaches the velocity of sound. Long before that value is reached, the eiliciency ot the venturi breaks down and the venturi no longer restores the air pressure. After leaving the throat of the venturi as the velocity decreases, the recovery of the pressure downstream does not take place and the efliciency oi' the carburetor breaks down.

If this inefficiency of the first venturi is made use or in order to control the admission of air from the second stage venturi then the recovery 1 efficiency will be maintained at a satisfactory level. As a venturi which will pass 10,000 pounds of air per hour at sea level will onlypass, say 3,000 pounds of air per hour at 35,000 feet, I propose to utilize this lack of efliciency as measured by pressure drop acres the venturi to bring into operation another venturi to help the flrst' venturi supply the necessary volume of air required at altitude. v v In the drawing, i is the main air entrance to take care of air of the primary venturi I 8. I2 is a smaller venturi which magnifies the eflect of the main venturi and produces a pressure drop utilized in metering the fuel supply. I 3 is the throttle in the outlet from the venturi ll, manually controlled by a throttle lever l4. The difl'erence of pressure created by the double venturi ii and I2 is transmitted to chambers I5 and Hi. This pressure difference acts on the diaphragm i! which separates the two'chambers l5 and I6. A rod I8 is connected to the diaphragm i1 and transmits motion therefrom to a fuel entrance valve 19.

Fuel enters under pressure from a passage 20 into-a vapor separator chamber iii in which there fuel from the chamber 24 to the passage 21. The

first valve 29 is used only for idling and is normally inoperative-when the engine is developing power and the valve is in the position shown. Valve 30 is a manual control needle which controls the jet 32 known as the'cruising jet. 3i is an automatically operated valve which controls the extra fuel for excess power needed when taking on to prevent over-heating. The orifice 33 which limits the eiiect of the valve 3| is known as the auxiliary take-oil Jet. These elements are all well known and have been in general use for some years.

Considering further the air entrance ill to the venturis II' and I2, thereare a series of openings 34 located on the downstream side of the throat of the venturi ll communicating with the cham-.

ber 35, which chamber 35 communicates through a passage 36 with a chamber 31 in which there is located a compression spring 38 connected to a. diaphragm 38 connected to a valve 40 which controls the admission of compressed air from a passage 4!. A convenient source of compressed air is the supercharger of the engine. The valve 40 is caused to act as a snap-over valve by means a of the. lever 42 and the tension spring 43. The compressed air admitted in the pipe 4| is conducted to the chamber 44, the right-hand side of which is formed by the diaphragm 45. On the right-hand side of the diaphragm 45 a' compression spring is located. A link 41 connects the diaphragm 45 with a throttle lever 48, controlling the throttle 49. The atmospheric pressure acts on the right-hand side of the diaphragm 45.

A second venturi is provided through which the air passes to the throttle 49. In this venturi 50 there is concentrically located a small venturi 5|. This double venturi 505i creates a pressure difference which is applied to the diaphragm 54 separating the two chambers 52 and 53, the atmospheric pressure existing in the air entrance to the second-stage venturi 50 being applied to Operation The normal operation of the carburetor when the throttle I3 is flmctioning alone follows the operation of the well-known pressure type airplane carburetor. When the throttle I3 is opened at such a point that the depression in the Venturi II no longer makes a sufllciently complete recovery, then there is a big enough drop across the venturi I to caus the diaphragm 39 to move to the right and to stretch the spring 43 and cause the valve 40 to snap into the open position. Compressed air i thereupon admitted from the supercharger connected at the pipe 4| to the chamber 44 and the diaphragm 45 is thus moved to the right, thereby opening th throttle 49 clockwise. This reduces the flow through the Venturi "-42 and if it were not for the valve mechanism 4|, 42 and 43, there would be a tendency for the engine to hunt." However, the valve is so constructed that as the throttle i3 is opened wide at high altitude, additional air is admitted through venturi 50 so that the breathing capacity of the engine is greater due to the larger air entrance at altitude than at sea level. The advantage of this construction is that at high altitude, the same weight of air is needed as on the ground but, of course, a much larger volume is needed. Thi is particularly true -when the superchargers are all located between the carburetor and the inlet valve. The additional fuel to supply the additional air is provided by the pressure difference between the chambers 52 and 53, acting on the diaphragm 54, which pressure tends to open valve IS. The air flow through double Venturi 50-5l creates pressure difierences, which, acting on diaphragm 54, push the valv I9 to the right so that there is a larger fuel flow past the valves 30 and 3| in order to balance the air flow.

The altitude correction device 55-56 is of a well known type and is adapted to correct the mixture ratio, controlled by the primary Venturi. When the second venturi comes into operation, this altitude correction continues to function.

An additional altitude valve 6| operated by the barometric element 82, provides the correction required at extreme altitudes.

What I claim is:

1. In an airplane carburetor of the pressure type having primary and secondary air entrances, Venturi tubes arranged in parallel therein, primary and secondary throttles therefor, manual control means for said primary throttle, automatic control means for said second throttle comprising means responsive to the drop in pressure in said primary air entrance, a fuel supply valve, interdependent means independently subjected to the air pressure produced by the Venturi tubes in said air passages due to the flow of air in each 01' said air entrances acting jointly and adapted to control the fuel supply valve, means responsive to the fuel flow for creating a pressure difference cooperating with the means responsive to air flow whereby said pressure differences due to fuel flow is adapted to oppose the sum of the pressure differences due to air flow in the primary and secondary air entrances, said opposing flow responsive mean being connected to said fuel supply valve whereby the balancing oftithe opp sing pressures controls the mixture ra o.

2. In an airplane carburetor of the pressure type having similar primary and secondary air venturis arranged in parallel, primary and secondary throttles in the exits therefrom, manual control means for said primary throttle, automatic control means for said second throttle comprising mean responsive to the drop in pressure between the entrance and exit of said primary Venturi due to the flow through said primary air venturi, a fuel supply valve, interdependent means independently subjected to the air pressures produced by the Venturi tubes in said air passages due to the flow of air in each of said air entrances acting jointly to control the fuel supply valve, means responsive to fuel flow for creating a pressure difierence cooperating with the means responsive to air flow whereby said pressure difference due to fuel flow is adapted to oppose the sum of the pressure differences due to air flow in the primary and secondary air entrances, said opposing flow responsive means being connected to said fuel supply valve whereby the balancing of the opposing pressures controls the mixture ratio.

STANLEY M. UDALE. 

